This invention relates to wire-stitching machines that staple together catalogs, magazines, and the like. More particularly, this invention relates to a method and apparatus for sensing movement of wire through the stitching machine and, in response to the sensing, controlling the operation of stitching heads within the stitching machine.
Magazines, catalogs, and other like articles are today bound automatically by high-speed wire stitching machines. The articles are assembled from printed sheets that are dropped from spaced-apart chutes onto a conveyer to form a stack. The stack is conveyed under one or more stitching heads that drive metal staples through the center of each stack, thereby binding the stack into an article. The article is then conveyed to an automatic bundler for mailing. The complete process requires no manual assistance. A stitching machine may further include means for diverting articles that are oversized or incorrectly stacked. The oversized article is allowed to pass beneath the stitching heads without being stapled and then is diverted through a diversion gate away from the bundler.
Present stitching machines, however, lack automatic means for sensing the availability of wire for the stitching heads. Typically, the wire is pulled by the stitching head from large spools. If the wire breaks or jams, the stitching head continues to attempt to staple the article, but without success. Articles may pass through the stitching heads without being bound and onto the bundler, where the lack of staples is often not discovered until after the articles are bundled and ready for mailing.
Several attempts have been made to correct this problem, all of which have disadvantages. A simple approach is to inspect manually the articles before they are bundled for mailing, as was often done before the development of automated bundlers. But manual inspection is time consuming, costly, and unreliable.
Another approach senses whether a staple has been driven correctly through the assembled sheets of the publication, such as is disclosed in U.S. Defensive Publication No. T958,003 to Russel et al. The Russel device senses electrically the presence of the two legs of the staple driven through the article. If the sensor detects only one leg, it alerts the operator. But the device does not sense the complete absence of a staple. If wire was not fed to the stitching head, the Russel device would not sense the problem because it relies on contact with at least one staple leg to alert the operator.
A third approach senses the supply of wire at the source, such as is shown in U.S. Pat. No. 4,516,713 to Meijer. The Meijer device comprises a lever biased by a spring to press against wire coiled on a spool. When the coiled wire remaining on the spool falls below a predetermined low level, the lever disengages from the wire and activates a sensor. This sensor, however, cannot detect stoppage of the wire movement to the stitching head caused by a jam or break. Similarly, U.S. Pat. No. 2,227,303 to Flaws, Jr. discloses a wire level sensor of a different form that suffers from the same drawback.
A need, therefore, remains for a means to sense a lack of wire movement to the stitching heads and for stopping the operation of the heads when the movement ceases.